Rotational method for making a metal melting crucible



Dec. 21, 1965 w, cou 3,225,130

ROTATIONAL METHOD FOR MAKING A METAL MELTING CRUCIBLE Filed July 31, 1962 2 Sheets-Sheet 1 IN VEN TOR JOHN (J- COHRTN Y Dec. 21, 1965 J. w. COURTNEY 3,225,130

ROTATIONAL METHOD FOR MAKING A METAL MELTING CRUGIBLE Filed July 51, 1962 2 Sheets-Sheet 2 IN VEN TOR JOHN (J. COURTNEY CZ'fz orneys.

United States Patent 3,225,130 ROTATIONAL METHOD FOR MAKING A METAL MELTING CRUCIBLE John W. Courtney, Dearborn, Mich, assignor to Electro Refractories & Abrasives Corporation, Buffalo, N.Y. Filed July 31, 1962, Ser. No. 213,701 4 Claims. ((31. 264-312) This invention pertains to a method for making crucibles for the melting of such metals as aluminum, brass, copper and the like and to a method of making them. This application is continuation-in-part of my applications 803,707 filed April 2, 1959, and 34,963 filed June 9, 1960, now both abandoned.

Such crucibles are commonly made of flake graphite bonded with clay or carbon introduced in the mix as tar or pitch made in general accord with US. Patents 1,356,939; 1,458,724; 1,458,726 and 1,479,107. My invention is applicable with all these compositions or many others but its advantages are particularly great when it is applied to compositions containing 50% or more by weight of material such as flake graphite and/or silicon carbide, which are characterized by a thin, flat (e.g. flake) particle shape and where the binder is of a plastic nature so that the mix flows under pressure resulting in orientation of the flat particles therein.

In the manufacture of crucibles, American practice has been to provide a smooth outer metal shell of a general barrel shape in which the material to form the crucible is placed and then by means of a paddle or roller to force the crucible material up around the inner face of the shell and compact it there to form a crucible wall from perhaps 1 /2 to 3 inches in thickness depending upon the size of the crucible.

This process, frequently called spinning or jiggering, tends to overlay successive laminar layers of material over one another in which layers the flat flakes or crystals tend to become oriented parallel to the face of the crucible with potential fissures or at least planes of weakness between successive layers. The wall is however tightly compacted and these slip planes between layers do not become apparent to the eye even when, as is often the case, they taper into the exposed surface inside the crucible causing it to be prematurely discarded as a leaker, or metal which has permeated these slip planes may freeze within the wall between heats and on reheating expand, wedging the layers of the wall apart and ultimately causing disintegration of the crucible.

After the crucible is formed to the desired shape, particularly with a tar or pitch bonded body, it is usually packed tightly in sand to support it and fired to drive off volatiles and give a permanent strong bond. Particularly in the case of carbon bonded bodies made from tar or pitch binder the escaping volatiles sometimes push the successive layers of material further apart, leaving wider fissures between them and facilitating the destructive actions above noted even though the entrances to the fissures are still not apparent to the eye at the surface of the crucible.

I have discovered that it is possible to almost completely overcome the formation of weak planes and incipient fissures within the wall of my crucibles by making the mold face of corrugated form and spinning the crucible mix against this corrugated face in the usual manner. When this is done, the solid layers interknit firmly, bridging and destroying any separating gaps between them. As a result, crucibles of my corrugated form have been found longer lived in service and unusually free from the troubles which prematurely destroy their smooth counterparts.

It is however desirable that the interior of the crucible be not corrugated but smooth and even so as to permit "ice the ready detachment and removal of adhering slag and dross from operation which must be scraped out at frequent intervals, preferably at least daily. These materials accumulate mostly adjacent the top of the crucible and can be barred off downward toward the wider bilge of the crucible. Any internal corrugations would make this very diflicult so I make the inside of my crucibles as smooth as possible.

A further advantage of the corrugated outer surface on my crucibles is that when the crucible is placed as usual in a cylindrical furnace where it is heated by the flame from burning oil or gas which swirls around the crucible, the heat is more effectively removed from the enveloping flames, thus increasing the efficiency of utilization of the fuel. Also my corrugated construction permits the average thickness of the crucible wall to be reduced, thus improving the transmission of heat through it to the metal inside so that melting :is more rapid. Practice has shown that the melting time. per charge of metal, and thereby the amount of metal which can be processed per day in a given furnace, is increased by one-fourth to one-third by the use of my new type of crucible. A further advantage of the reduced wall thickness is that it makes the crucible lighter and easier for a workman to handle in cases Where it is removed bodily from the furnace when full of metal for pouring.

In illustration of my invention, in the accompanying drawings:

FIG. 1 is a side elevation of a crucible embodying this invention:

FIG. 2 is a top plan view thereof:

FIG. 3 is a top view of a sectional mold for the manufacture of crucibles embodying my invention:

FIG. 4 is a sectional view of said mold along line 44 of FIG. 3 as assembled with accessory equipment and mix for use.

I accomplish my objectives by providing a corrugated surface on the outside of the crucible, the corrugations usually extending laterally rather than vertically parallel to the axis of the crucible. I prefer that the corrugations form a helix around the crucible so that the thin part of the wall on one side is directly opposite a thick part on the other side in order that no plane of weakness perpendicular to the axis shall result, although I do not broadly limit my invention to this helical disposition of the corrugations. I prefer also that the corrugations be omitted adjacent the bottom and top of the crucible, leaving walls of full thickness at those points for a distance along the wall at least equal to the thickness of the crucible wall. This is because I find that lamination at these points is less prevalent than in the intervening area and additional thickness is desired here to impart strength for handling and for resistance to surface slag cutting.

In order that my invention may be more readily understood, I have illustrated it in the accompanying FIGURE 1 showing a partial section cut through one of my crucibles along a plane passing through the axis thereof.

In this figure, 1 designates the crucible in general, comprising a lateral wall 2 and a bottom 3. The inside 4 of the lateral wall constitutes a smooth curve of the shape usual in crucibles. The outside of this wall is however corrugated in a series of hills 5 and valleys 6. Due to the helical nature of the corrugation, the point 8 on the outer wall diametrically opposite point 6 is the summit of a hill, while point 7 (opposite hill 5') falls in a valley. At the upper edge 9 of the crucible, I do not extend my valley to the edge of the crucible but rather leave this edge with the thickness corresponding to the hills all the way around its circumference. Similarly at the base, I discontinue my valley before reaching the extreme corner 10.

In order that the troublesome laminations be eliminated, the corrugations in the wall must be of substantial depth and sharpness while in order to maintain adequate wall strength they must not be too deep. By practical experimentation I find that the wall thickness adjacent the valleys should be from 50 to 80% of that adajcent the hills i.e. the depth of the groove is from 20 to 50% of the thickness of the crucible wall between grooves therein. I find also that the cross section of the corrugations should not be too sharply angular but rather may advantageously be a smooth approximately sinusoidal curve where the distance from the top of one hill to the top of the next is from four to seven times the depth of the corrugation from hill top to valley bottom, a ratio of approximately five to one being preferred.

The following is one specific example of the procedure used in the manufacture of one of my crucibles, cited as an illustration and not as a limitation:

For my mold, I form side walls of a strong aluminum alloy in the form of a vertical barrel 11 cut into three vertically divided sections 11a, 11b and 110 which can be easily pulled away from the crucible after molding. These are held firmly together by dowels and suitable bands or clamps and are fitted snugly into a surrounding holder 12 at their bottom end. This holder is driven by shaft 13 to cause the mold to rotate in the direction of the arrow in FIG. 3 around its axis. The wall sections do not extend across the bottom of the holder but the bottom of the crucible is rather formed directly against the top horizontal face 14 of the surrounding holder which thus is a part of the mold.

The interior of this vertical barrel is corrugated with sinusoidal grooves 15, which in a typical case are spaced 2 /2 inches from crest to crest and /2 inch deep. These grooves do not extend into the areas 4 inches from the top and bottom of the barrel respectively.

In use, a portion of the mix to be formed (roughly onehalf to two-thirds of the total required) is placed in the bottom of the barrel and rotation is begun. Meanwhile a forming tool 16 having a face shaped with the contour of the desired inner face of the crucible is inserted in the center of the barrel from above and forced down into the pile of loose mix 17 in the bottom thereof and is thereafter moved sidewise. This results in displacement of the mix toward and up along the inner wall of the barrel where it is squeezed into the grooves and builds up along the wall of the barrel. Additional loose mix is added in the barrel from time to time and is thus successively squeezed against and added to the crucible wall, being built up until the desired thickness is accumulated, the outer face of the crucible next to the mold barrel being corrugated and the inner face next to the forming tool being a smooth surface of revolution. By positioning the forming'tool 16 the bottom and side of the crucible being formed may be built to any desired thickness. A top plate 18 shown in FIG. 4 but not FIG. 3 is usually provided against which to form the top edge of the crucible during rotation or the top edge may be trimmed smooth with a knife.

After forming is complete, the mold barrel 11 with the crucible contained in it is lifted out of the surrounding holder 12 and set on a support on which the crucible is to be fired. The split barrel is then opened and pulled away from the formed crucible which is thereafter supported for firing and fired in the usual way.

As noted above, my invention can be used for crucibles of any of many standard compositions, the particular choice of materials not being a part of my invention, but it is particularly useful with mixes in which the proportion of fiat shaped particles is so great as to tend to result in laminations within the wall when the mix is spun into shape. 7

Having thus illustrated and described my invention, what I claim is:

1. In the manufacture of crucibles, the method which consists of:

(a) providing an open top closed bottom cylindrical split mold having a helical corrugated surface;

(b) charging said mold with a mix containing at least fifty percent by weight of particles of flat shape and plastic binder therefor;

(c) inserting an elongated forming tool having a forming edge into said mold and into engagement with said mix, said forming edge being disposed a distance from said mold surface equal to the desired wall thickness of said crucible;

(d) rotating said mold and said forming tool with respect to each other so that the mix is forced outward and packed against said corrugated mold surface;

(e) successively adding additional mix until the entire crucible wall has been formed;

(f) removing said forming tool; and

(g) pulling said split mold apart to free said crucible formed in the mold.

2. The method of claim 1, wherein:

(a) the corrugations of the mold are approximately sinusoidal, the distance across the corrugations being from four to seven times the depth of the corrugations; and

(b) the depth of the corrugation is from 20 to 50% of the thickness of the intended crucible wall.

3. The method of claim 1, wherein:

(a) said particles are material selected from the group composed of graphite and silicon carbide.

4. A method of making a crucible of refractory material by spinning, wherein weak planes and incipient fissures between laminar layers of the crucible wall are eliminated, comprising the steps of:

(a) assembling a generally barrel-shaped cavity mold,

the walls of which have circumferential corrugations;

(b) depositing within the cavity a portion of the total amount of mix required to make the finished product, said mix comprising at least 50% of material selected from the group consisting of flake graphite and silicon carbide and the plastic binder therefor;

(c) inserting within the mold cavity a forming tool having a shape corresponding to that desired for the inner wall of the crucible, said tool being inserted into the loose mix;

(d) repeatedly rotating the mold with respect to the forming tool;

(e) pressing said tool against the mix with sufficient force to compact the mix within the corrugations of the cavity wall;

(f) adding additional mix until the desired wall thickness is achieved; and

(g) exerting sufiicient outward force against the mix by said tool to cause interknitting of the layers of mix comprising the crucible wall, thus eliminating planes of weakness as a result of the mix being forced against the corrugations of the mold cavity.

ROBERT F. WHITE, Primary Examiner.

MORRIS WOLK, Examiner. 

1. IN THE MANUFACTURE OF CRUCIBLES, THE METHOD WHICH CONSISTS OF: (A) PROVIDING AN OPEN TOP CLOSED BOTTOM CYLINDRICAL SPLIT MOLD HAVING A HELICAL CORRUGATED SURFACE; (B) CHARGING SAID MOLD WITH A MIX CONTAINING AT LEAST FIFTY PERCENT BY WEIGHT OF PARTICLES OF FLAT SHAPE AND PLASTIC BINDER THEREFOR; (C) INSERTING AN ELONGATED FORMING TOOL HAVING A FORMING EDGE INTO SAID MOLD AND INTO ENGAGEMENT WITH SAID MIX, SAID FORMING EDGE BEING DISPOSED A DISTANCE FROM SAID MOLD SURFACE EQUAL TO THE DESIRED WALL THICKNESS OF SAID CRUCIBLE; (D) ROTATING SAID MOLD AND SAID FORMING TOOL WITH RESPECT TO EACH OTHER SO THAT THE MIX IS FORCED OUTWARD AND PACKED AGAINST SAID CORRUGATED MOLD SURFACE; (E) SUCCESSIVELY ADDING ADDITIONAL MIX UNTIL THE ENTIRE CRUCIBLE WALL HAS BEEN FORMED; (F) REMOVING SAID FORMING TOOL; AND (G) PULLING SAID SPLIT MOLD APART TO FREE SAID CRUCIBLE FORMED IN THE MOLD. 